Andrew C. Metaxas

Numerical modelling of atmospheric pressure gas discharges leading to plasma production

In this paper, we give a detailed review of recent work carried out on the numerical characterization of non-thermal gas discharge plasmas in air at atmospheric pressure. First, we briefly describe the theory of discharge development for dielectric barrier discharges, which is central to the production of non-equilibrium plasma, and we present a hydrodynamic model to approximate the evolution of charge densities. The model consists of the continuity equations for electrons, positive and negative ions coupled to Poissons equation for the electric field. We then describe features of the finite element flux corrected transport algorithm, which has been developed to specifically aim for accuracy (no spurious diffusion or oscillations), efficiency (through the use of unstructured grids) and ease of extension to complex 3D geometries in the framework of the hydrodynamic model in gas discharges. We summarize the numerical work done by other authors who have applied different methods to various models and then we present highlights of our own work, which includes code validation, comparisons with existing results and modelling of radio frequency systems, dc discharges, secondary effects such as photoionization and plasma production in the presence of dielectrics. The extension of the code to 3D for more realistic simulations is demonstrated together with the adaptive meshing technique, which serves to achieve higher efficiency. Finally, we illustrate the versatility of our scheme by using it to simulate the transition from non-thermal to thermal discharges.We conclude that numerical modelling and, in particular, the extension to 3D can be used to shed new light on the processes involved with the production and control of atmospheric plasma, which plays an important role in a host of emerging technologies.

Three-dimensional numerical modelling of gas discharges at atmospheric pressure incorporating photoionization phenomena

A three-dimensional (3D) numerical model for the characterization of gas discharges in air at atmospheric pressure incorporating photoionization through the solution of the Helmholtz equation is presented. Initially, comparisons with a two-dimensional (2D) axi-symmetric model are performed in order to assess the validity of the model. Subsequently several discharge instabilities (plasma spots and low pressure inhomogeneities) are considered in order to study their effect on streamer branching and off-axis propagation. Depending on the magnitude and position of the plasma spot, deformations and off-axis propagation of the main discharge channel were obtained. No tendency for branching in small (of the order of 0.1 cm) overvolted discharge gaps was observed.

Simulation for the transition from non-thermal to thermal discharges

A numerical algorithm is presented that characterizes the transition from non-thermal to thermal high-pressure gas discharges. To achieve this, the Poisson, charged particle continuity and Navier–Stokes equations are coupled together to analyse the interaction between the charged and neutral particles and the electric field. In this work, a new Navier–Stokes solver is developed based on the finite-element flux-corrected-transport method. This solver studies the movement of the neutral gas particles by solving the conservation of mass, momentum and energy for viscous fluids. The solver is thoroughly tested in both two-dimensional Cartesian and cylindrical axisymmetric coordinates. After validation, it is coupled to an existing Poisson and charged particle continuity solver through production and loss processes, momentum energy transfer and Joule heating effects. The avalanche and streamer discharges are analysed starting from a single electron and positive ion as initial conditions. Finally, the effect of including heating of the neutral gas on the electron density is discussed.

New high quality adaptive mesh generator utilized in modelling plasma streamer propagation at atmospheric pressures

A new adaptive mesh generator has been developed and used in the analysis of high-pressure gas discharges, such as avalanches and streamers, reducing computational times and computer memory needs significantly. The new adaptive mesh generator developed, uses normalized error indicators, varying from 0 to 1, to guarantee optimal mesh resolution for all carriers involved in the analysis. Furthermore, it uses h- and r-refinement techniques such as mesh jiggling, edge swapping and node addition/removal to develop an element quality improvement algorithm that improves the mesh quality significantly and a fast and accurate algorithm for interpolation between meshes. Finally, the mesh generator is applied in the characterization of the transition from a single electron to the avalanche and streamer discharges in high-voltage, high-pressure gas discharges for dc 1?mm gaps, RF 1?cm point?plane gaps and parallel-plate 40?MHz configurations, in ambient atmospheric air.

Three-Dimensional Streamer Modeling in Atmospheric Pressure Air

A 3-D streamer model that incorporates photoionization phenomena in atmospheric pressure air has been developed. It is applied to both point-plane and plane-plane electrode configurations in order to examine phenomena that have no cylindrical symmetry. The role of spontaneously distributed plasma spots in the propagation path of a streamer in discharge branching is then analyzed. Streamer advancement that ignites from a sharp point electrode is also presented in a full 3-D simulation. Images of the electron density evolution in the interelectrode space for the aforementioned configurations when the plasma spots interact with the streamer head are presented.